Velocity modulation electron discharge device



March 24, 1953 E. D. MGARTHUR VELOCITY MODULATION ELECTRON DISCHARGE DEVICE Filed Dec. 31, 1949 Inventor": Ehnev" D. McArbhuY;

W4-fiz0 by His Attorney.

Patented Mar. 24, 1953 VELOCITY MODULATION ELECTRON DISCHARGE DEVICE Elmer D. McArthur, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application December 31, 1949, Serial No. 136,297-

1 Claim. 1

My invention relates to an ultra high frequency electron discharge device of the type employing a'velocity modulated electron beam.

It is known that an electron beam may be velocity modulated by an ultra high frequency input signal and that a beam so modulated may be curved by a static deflecting field, the radius of curvature of the beam being a function of its velocity. By employing an output resonator adapted to be excited at the frequencyof the deflections of the modulated beam, an amplified output signal may be obtained. Discharge devices of this type, however, while suitable for operation as laboratory apparatus, have not found general application in ultra high frequency systems, due in part to difiiculty and inconvenience encountered in their manufacture and application.

It is an object of my invention to provide an improved ultra high frequency amplifier of a type employing a velocity modulated electron beam.

According to the illustrated embodiment of my invention a curved conducting member defining the outer boundary of the curved path of an electron beam is employed in an ultra high frequency amplifier of the nature described. One or more pairs of cavity resonators are incorporated in the curved member near the origin of the electron beam, the resonators having slotlike excitation gaps communicating with the electron beam path so that the fringing electric fields produced across the gaps when the input resonator system is excited extend into the elec tron path to velocity modulate the beam. A corresponding pair or pairs of output resonators are incorporated in the curved member at a region where the electron beam has been substantially curved so that the resonators are excited by the electron beam deflections as the beam curvature varies with the input voltage. A second curved conductive member is positioned along the inner boundary of the curved path and positive potentials are applied to the inner and outer curved members to collect the electrons not utilized in operation of the amplifier and to reduce the delelowingdescription taken in connection with the drawings in which Fig. 1 is an enlarged cross section view of an electron discharge device embodying my invention, and Fig. 2 is a sectional view along line A-A of Fig. 1.

Referring now to the principal elements of the embodiment shown in Fig. 1, an electron;

gun assembly I is employed for producing an electron beam which is suitably curved in an 6 approximately semi-circular path 2 by a static,

magnetic field perpendicular to the plane of the drawing and suitably provided by a permanent magnet in Fig. 2 having its north and south pole faces respectively "positioned on either side of In Fig. 1 the lines of magthe discharge device. netic flux may be considered as perpendicular to the drawing and directed into it. A curved conducting member 3 is disposed along the outerboundary of the curved electron path .2 and incorporates an input resonator system 4 near the.-

A corre sponding output resonator system 5 is similarly beginning of the electron path 2.

incorporated in the member 3 near the end of the electron path, which path is terminated by a transversely extending face 6 of the curved member '3, the surf-ace 6 acting as a collector electrode.

is provided to help collect the nonuseful electrons, including those secondarily emitted; The

entire device is enclosed in an envelope comprising a metallic base plate 8 and a metallic casing 9 surrounding the assembly and hermetically se'-; cured to the base 8, as further shown in-Fig. 2.

Referring'again to Fig. 1 for a detailed de--..l' scription of my invention, the electron gu'n-asa;

sembly I may'suitably take the form of" a bathode IO having an emitting surface, such as a" coating of alkaline earth oxides, and a heater element H adjacent the cathode surface, 'the cathode being mounted on an insulating support,

member I2. A beam accelerating electrode l3,

which may suitably take the form of an aper-' tured metallic cylindrical cupsurrounding the cathode with its open end secured to the elecably made of copper, is secured at its ends to the.

base plate 8 and the inner curved member 1, like In cooperation with the curved mem-- her 3, a second curved conductingmember I adjacent the inner boundary of the electron path 2 insulatingly sealed through the base plate 8 to mission line H, whose outer conductor is secured to the base plate 8 and whose inner conductor extends therethrcugh and through a bore in the curved member 3 to be conventionally coupled with the resonator I5, may be employed. By reason of end space coupling of resonator I 5 with resonator I6 the input system may be made to resonate and hence present fringing ultra, high frequency electric fields across the resonator gaps and substantially tangent to the electron path 2. Electrons in time phase with the fringing electric field of either resonator are thus accelerated and those a half cycle later in time are decelerated. Since the resonators alternate in polarity with respect to each other as in a 11' mode magnetron, the respective resonator excitation gaps, that is the location of the resonator slots on the inner curved surface of the member 3, are s spaced that the resonators Work in unison to modulate the electrons, resonator I6 thus further accelerating and decelerating those electrons respectively accelerated and decelerated by resonator I5. This spacing is such that the electron transit angle between the resonators is one half cycle, or equivalent to the product of one half period at the resonator frequency times the beam velocity. At any instant during operation the metal segment of the curved member 3 between the slot portions of resonators I5 and I6 has the same ultra high frequency potential on the portion defining a surface of the slot of resonator I5 as on the portion defining a surface of the slot of resonator I5. Accordingly, the input resonator system may be considered as operating with that portion of the member 3 comprising the segment between resonators I5 and I5 alternately comprising the common positive and the common negative terminal for both resonators and having a potential with respect to the remainder of the curved member 3 equivalent to either resonator voltage, thus substantially isolating the ultra high frequency voltage variations to the relatively small segment.

The output resonator system 5 comprises a second pair of hole and slot cavity resonators I8 and I9 incorporated in the curved member 3 near the end of the semi-circular electron path and having their excitation gaps, communicating with the electron path. The substantial spacing of the output resonator system 5 from the input system 4 aids in minimizing coupling between them as well as providing for more effective excitation of the output system due to the greater radial deflection of the electron beam corresponding to its greater total curvature. In operation, the path radius changes from a maximum value, where the beam is close to the output gaps for the highest velocity electrons, to a smaller value for lowest velocity electrons when the beam is remote from output gaps. The excitation of the output resonators accordingly varies with the proximity of the electron beam to the resonator gaps and the energy of the electron beam is thus utilized to amplify the ultra high frequency input signal.

The induced output energy may be suitably coupled to a utilization means by conventional coupling arrangements, such as a concentric transmission line 20 having its outer conductor secured to the base 9 and its inner conductor extending therethrough and through a bore in the curved member 3 to be coupled at its inner end to the end resonator I9. As in the input system, the output resonators I8 and I 9 are spaced apart the same distance as the input resonators I5 and I6 and are coupled together through the end spaces on either side of the resonators to work in unison. Again, while at any instant of time the voltage across the successive gaps may be considered as alternating in polarity, the segment between the output gaps can also be considered as alone varying in potential with respect to the remainder of the curved member 3. Accordingly, the input and output resonator systems need not be insulated from each other for efficient operation, although incorporated in a unitary structure, with the resultant advantages in case of construction and elimination of adjustment.

The inner and outer curved members 3 and I serve an important function in removing secondarily emitted electrons and unwanted electrons from the beam. I preferably apply a potential to both curved electrode members which is positive with respect to the cathode, with the potential on the outer member being the more positive. The transversely extending portion 6 of the member 3 which extends across the electron path 2 at a point beyond the last output resonator I9 collects the electrons of the beam after they have performed their function of exciting the output system. The unwanted electrons which have been decelerated by the velocity modulated input system may either be collected on the surface of the inner curved member 1 or in an electron trap 2I incorporated in the member I near the end of the semi-circular beam path. This trap may be readily formed by recessing a portion of the inner member surface leaving an outer wall portion between the recess and the electron beam. Those electrons which have been decelerated tend to fall into the recessed portion and secondary emission from them is more readily confined. Spurious efiects due to the secondarily emitted electrons caused by the electrons striking the anode surface 5 are minimized due to their attraction to the nearby surfaces having positive potentials.

While I have described my invention as employing a conventional magnetic deflection field to curve the electron beam, the discharge device can be utilized so that the electron beam is deflected by an electric deflecting field. To form such a field, the inner conducting member is maintained at a substantial positive potential with respect to the outer member, both members being positive with respect to the electron beam to collect unwanted electrons, thus exerting a centripetal force on the electrons emitted from the cathode.

In addition, it is also obvious that Without departing from the spirit of my invention a greater number of input and output resonators may be employed, the essential features of combining the input and output resonators in a .curved unitary conductive member, which also serves to collect unwanted electrons, being preserved and the output resonators being adapted to be excited according to the varying extent of the deflection of the modulated electron beam toward the interaction gaps of the resonator.

' While the present invention has been described by reference to particular embodiments thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the invention. I, therefore, aim in the appended claim to cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is:

An ultra high frequency discharge device amplifier having an electron gun for producing an electron beam, means positioned along the path of said beam for producing a static magnetic field normal to said path to'defiect said electron beam into a curved path corresponding to an approxionator system comprising a pair of spaced cavity resonators incorporated in said first curved member near the beginning of said curved path and communicating therewith, means coupled to one of said resonators of said input resonator system for exciting said input system from an ultra high frequency signal source to produce cooperating fringing electric fields extending into said electron path and having substantial components tangent thereto for varying the beam radius of curvature by modulating its velocity, an output resonator system comprising a pair of spaced cavity resonators incorporated in said first curved member near said end of said path and communicating with said path in order to be excited in unison by the varying proximity of said electron beam according to its radius of curvature, and a concentric transmission line coupled to one of said resonators of said output resonator system.

ELMER D. MCARTHUR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,469,964 Hartman May 10, 1949 2,470,856 Kusch May 24, 1949 2,511,407 Kleen et a1 June 13, 1950 2,566,087 Lerbs Aug. 28, 1951 2582.185 Willshaw Jan. 8, 1952 

